Wirelessly posted (BlackBerry8530/5.0.0.1030 Profile/MIDP-2.1 Configuration/CLDC-1.1 VendorID/417)
I do not know if it is still the case, but not long ago, some Avis locations were charging considerably more for a full seven-day (168-hour) rental, than for a six-day, 23-hour (167-hour) rental. It's always best to do a comparison before finalizing the booking.
And as recently noted in the FT Avis forum, some Avis Manhattan locations are charging more if you return a car sooner (or later) than agreed to, even if you are staying within the same number of rental days.